Mats Carlsson

Colloidal processing of Al2O3-based composites reinforced with TiN and TiC particulates, whiskers and nanoparticles

A whisker is a common name of single crystalline inorganic fibre of small dimensions, typically 0.5-1 μm in diameter and 20-50 μm in length. Whiskers are mainly used as reinforcement of ceramics. This work describes the synthesis and characterisation of new whisker types. Ti0.33Ta0.33Nb0.33CxN1-x, TiB2, B4C, and LaxCe1-xB6 have been prepared by carbothermal vapour–liquid–solid (CTR-VLS) growth mechanisms in the temperature range 900-1800°C, in argon or nitrogen. Generally, carbon and different suitable oxides were used as whisker precursors. The oxides reacted via a carbothermal reduction process. A halogenide salt was added to form gaseous metal halogenides or oxohalogenides and small amount of a transition metal was added to catalyse the whisker growth. In this mechanism, the whisker constituents are dissolved into the catalyst, in liquid phase, which becomes supersaturated. Then a whisker could nucleate and grow out under continuous feed of constituents. The syntheses of TiC, TiB2, and B4C were followed at ordinary synthesis conditions by means of mass spectrometry (MS), thermogravimetry (TG), differential thermal analysis (DTA) and quenching. The main reaction starting temperatures and reaction time for the different mixtures was revealed, and it was found that the temperature inside the crucible during the reactions was up to 100°C below the furnace set-point, due to endothermic nature of the reactions. Quench experiments showed that whiskers were formed already when reaching the temperature plateau, but the yield increased fast with the holding time and reached a maximum after about 20-30 minutes. Growth models for whisker formation have been proposed.Alumina based composites reinforced by (2-5 vol.%) TiCnano and TiNnano and 25 vol.% of carbide, and boride phases (whiskers and particulates of TiC, TiN, TaC, NbC, (Ti,Ta)C, (Ti,Ta,Nb)C, SiC, TiB2 and B4C) have been prepared by a developed aqueous colloidal processing route followed by hot pressing for 90 min at 1700°C, 28 MPa or SPS sintering for 5 minutes at 1200-1600°C and 75 MPa. Vickers indentation measurements showed that the lowest possible sintering temperature is to prefer from mechanical properties point of view. In the TiNnano composites the fracture mode was typically intergranular, while it was transgranular in the SiCnano composites. The whisker and particulate composites have been compared in terms of e.g. microstructure and mechanical properties. Generally, additions of whiskers yielded higher fracture toughness compared to particulates. Composites of commercially available SiC whiskers showed best mechanical properties with a low spread but all the other whisker phases, especially TiB2, exhibited a great potential as reinforcement materials.

Synthesis and characterisation of boron carbide whiskers and thin elongated platelets

Abstract Boron carbide whiskers and platelets have been synthesised via a carbothermal vapour–liquid–solid (VLS) growth mechanism starting with B 2 O 3 and carbon black as sources of boron and carbon, respectively. The reactions were studied in the temperature range 1200–1800°C, testing Co, Ni and Fe as catalyst metals. The best result was obtained at a synthesis temperature of 1700°C with a reaction mixture containing B 2 O 3 :C:NaCl:Co in the molar ratios of 1:6:0.25:0.1. The obtained boron carbide product exhibited different morphologies ranging from elongated platelets to whiskers with very high aspect ratio. Five different whisker-like crystal morphologies were found, and their growth directions and structural defects were characterised by means of transmission electron microscopy.

Vapour–liquid–solid growth of TiB2 whiskers

Whiskers of TiB2 have been synthesised via a carbothermal vapour–liquid–solid (VLS) growth mechanism. The whisker growth was investigated in the temperature region 1100–1800°C in argon. The best result was obtained with a starting mixture of TiO2:B2O3:C:NaCl:Ni in the molar ratios 1:1:6:0.25:0.1 at 1500°C. Thermogravimetric analyses and mass-spectroscopy measurements were used in studying the whisker growth. The obtained TiB2 whiskers are 0.5–2 μm in diameter and 10–50 μm in length. TEM studies of the whiskers showed that the dominating growth direction is temperature dependent.

The Gaze as constituent and annihilator

Abstract This article aims to join the contemporary effort to promote a psychoanalytic renaissance within cinema studies, post Post-Theory. In trying to shake off the burden of the 1970s film theorys distortion of the Lacanian Gaze, rejuvenating it with the strength of the Real and fusing it with Freudian thoughts on the uncanny, hopefully this new dawn can be reached. I aspire to conceptualize the Gaze in a straightforward manner. This in order to obtain an instrument for the identification of certain strategies within the filmic realm aimed at depicting the subjective destabilizing of diegetic characters as well as thwarting techniques directed at the spectorial subject. In setting this capricious Gaze against the uncanny phenomena described by Freud, we find that these two ideas easily intertwine into a draft description of a powerful, potentially reconstitutive force worth being highlighted. Mats Carlsson, Scholar at the Department of Media Studies, Cinema Studies, at Stockholm University. His academic interests revolve around (post-modern) critical theory, with the goal of applying theoretical strategies, such as psychoanalysis, as a limelight on the ideological implications inherent in todays media-saturated society.

Preparation and Characterization of Alumina Based TiNn and SiCn Composites

Abstract : Ceramic composites containing 2 and 5vol % of nanosized commercially available TiN and SiC particles in alumina were prepared via a water based slurry processing route followed by spark plasma sintering (SPS) at 75 MPa in the temperature range 1200-1600 deg. C. Some of the samples could be fully densified by use of SPS already after five minutes at 1200 deg. C and 75 MPa. The aim was to control the alumina grain growth and thus obtain different nano-structure types. The microstructures have been correlated to some mechanical properties; e.g. hardness and fracture toughness.